Spatial and temporal development of chondrocyte-seeded agarose constructs in free-swelling and dynamically loaded cultures

Dynamic deformational loading has been shown to significantly increase the development of material properties of chondrocyte-seeded agarose hydrogels, however little is known about the spatial development of the material properties within these constructs. In this study, a technique that combines video microscopy and optimized digital image correlation, was applied to assess the spatial development of material properties in tissue-engineered cartilage constructs cultured in free-swelling and dynamically-loaded conditions (3h/day, 5 days/week, and maintained in free-swelling conditions when not being loaded) over a 6-week period. Although homogeneous at day 0, both free-swelling and dynamically loaded samples progressively developed stiffer outer edges and a softer central region. The distribution of GAGs and collagens were shown to mimic this profile. These results indicate that although dynamic loading augments the development of bulk properties in these samples, possibly by overcoming some of the diffusion limitation and nutrient transport issues, the overall profile of construct properties in the axial direction remains qualitatively the same as in free-swelling culture conditions. Poisson's ratio of these constructs increased over time in culture with increased fixed charged density contributed by the GAGs, but this increase was significantly less in dynamically loaded samples by day 42. Polarized light microscopy of Picrosirius Red labeled samples, at an angle perpendicular to the direction of loading, suggests that these differences in Poisson's ratio may be due to improved organization of collagen network in the dynamically loaded samples.